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Geometry and Trigonometry
/ Lines, angles, and triangles
Difficulty: Easy
In the figure, line intersects lines and . Line is parallel to line . What is the value of ?
Explanation
The correct answer is . It's given that line is parallel to line . Since line intersects both lines and , it's a transversal. The angles in the figure marked as and are on the same side of the transversal, where one is an interior angle with line as a side, and the other is an exterior angle with line as a side. Thus, the marked angles are corresponding angles. When two parallel lines are intersected by a transversal, corresponding angles are congruent and, therefore, have equal measure. It follows that the value of is .